1. Field of the Invention
The present invention concerns run-flat tire systems. More particularly, the present invention concerns lubricants for run-flat tire systems. Even more particularly, the present invention pertains to thickened, dry and/or encapsulated lubricants for run-flat tire systems.
2. Prior Art
As is known to those skilled in the art to which the present invention pertains run-flat tires have become prevalent in automobiles to enable the vehicle to remain driveable over a sufficient distance to enable tire repair. Although there exists many configurations for such tires, one of the more promising run-flat tire systems comprises a tire, a wheel rim or wheel, and an interior support ring. The support ring, which is disposed interiorly of the tire, carries the vehicle weight if its associated tire loses pressure. In such instance, when the outside tire collapses it contacts the inner support ring. Typically, the inner support ring is disposed about one to three inches from the interior surface of the tire when the tire is fully inflated.
In order for such run-flat tire or tire system to be effective, it is essential that a lubricant be disposed between the exterior surface of the support ring and the inner surface of the tire. This lubricant is intended to prevent a temperature increase or reduce the rate of temperature increase to an acceptable level, i.e. a level low enough to prevent thermal degradation of any of the elastomeric components of the tire for the manufacturer's specified period of time under its specified conditions. This temperature rise is due to the friction between the support ring and the inner surface of the tire due to their relative motion caused by their differing diameters. Usually, the lubricant is intended to be deposited onto the interior surface of the tire.
Manufacturer's specifications, in addition to temperature increase parameters, require that the lubricant have a gel-like or grease-like consistency so that it will remain in place and not leak or flow while the tire remains in its inflated or non-run-flat condition.
Furthermore, in order for the lubricant to be environmentally acceptable in today's market, it is all but necessary that it be water-based. The art has addressed these issues and created thickened lubricants for meeting these criteria. However, these prior art lubricants still need major improvements. First, ordinarily from about 75 to about 300 grams of lubricant need to be applied to the inside of the tire. Under the best of conditions, this major quantity of the current lubricants required in order to provide an efficacious system, is unacceptable because of wheel balance requirements, cost of lubricant, etc.
Moreover, known run-flat tire thickened lubricants undergo a permanent thinning transformation and, thus, pour like the liquid starting material, when exposed to shear stresses or rubbing under pressure. The shear stress or rubbing occurs because the gap between the support ring and the tire is relatively small and the two occasionally make contact when driving over speed bumps, pot holes, curbs, and the like in a non-run-flat condition. This contact, eventually, causes these prior art lubricants to permanently revert back to a liquid state. After being liquefied by this intermittent contact, if the tire punctures, all of the lubricant runs out and the tire fails prematurely.
As will be detailed hereinafter, the present invention provides a thickened lubricant which is particularly adapted for utilization in a run-flat tire system.